Liquid light guide catheter having biocompatible liquid light guide medium

ABSTRACT

A catheter system to ablate target matter within a mammalian body using light energy is described. The system may include an open-ended catheter tip through which a liquid light guide medium flows to the target matter, where at least a portion of the liquid light guide medium exiting the catheter tip creates a fluid optical channel to transmit the light energy from the catheter tip to the target matter. The system may also include a catheter lumen whose distal end includes the open-ended catheter tip, a light source to generate the light energy, and a liquid light guide medium source fluidly coupled to the catheter lumen. The liquid light guide medium source may include a reservoir of the liquid light guide medium that includes a magnesium chloride solution or a lactated Ringer&#39;s solution.

CROSS-REFERENCES TO RELATED APPLICATIONS

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STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

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BACKGROUND OF THE INVENTION

Vascular occlusions restrict the flow of blood to tissue and organs andcan cause a variety of problems. For example, occlusions that restrictblood flow to the heart can cause heart attacks and angina, andocclusions that restrict blood flow in cerebral blood vessels (e.g.,cerebral arteries and veins) can cause strokes and other neurologicalproblems. It is therefore desirable that these occlusions be opened upand removed.

One approach to treating occlusions is to apply drugs that cause thevessel to dilate. However, these drugs are not suitable for allpatients, and even when they are suitable their ability to slow andreverse the occluding process is usually only temporary. Drugs may alsobe administered that dissolve occlusions. However, these drugs can causeserious side-effects, such as hemorrhaging, and do not dissolve manytypes of vascular occlusions.

Another approach to treating occlusions is angioplasty, where a device(typically a catheter) for dilating an occluded vessel is introducedthrough an opening in the skin and wall of a large vessel, such as thebrachial or femoral artery. When the device reaches the site of theocclusion, treatment is administered to break up or otherwise treat theocclusion. For example, in balloon angioplasty a guide wire firstreaches the site of the occlusion and guides a catheter lumen to thesite. The catheter lumen has an inflatable balloon near its tip thatinflates to compact the occlusion and stretch the walls of the vessel.Unfortunately, the results of balloon angioplasty can also be temporaryas the occluding process may continue and re-block the vessel.

Additional approaches to treating occlusions include recanalizing theocclusion by cutting and/or pulverizing the occlusion with a vascularcatheter. Here also guide wires may first reach the occlusion site andguide a catheter lumen to the occlusion. The guide wire tips aredesigned to be relatively small and stiff so that they can more easilypenetrate and advance through the occlusion, providing a path or railfor the subsequently advancing catheter to follow through the occlusion.When the catheter reaches the occlusion, a device at the catheter'sdistal tip is advanced into the occlusion where it performs theoperation to cross or penetrate the occlusion. The catheter may alsoinclude components that capture, suction or otherwise prevent theocclusion fragments from traveling downstream and creating anotherblockage. These approaches are relatively effective for treating acuteocclusions made of relatively soft tissue and occlusions that do notcompletely block the passage of blood and other fluids through thevessel, but are less effective for treating calcified, fibroticocclusions that are difficult to penetrate with conventional guidewires.

Vascular occlusions may also be treated by ablation with light energy(e.g., laser atherectomy). These approaches involve positioning opticalfibers at the site of the occlusion and delivering light energy throughthe fibers to ablate the occlusion. The optical fibers are typicallymade of fused silica or quartz, and are fairly inflexible unless theyare made very thin. Unfortunately, thin optical fibers can only deliversmall amounts of light energy to the occlusion site. Also, the thindelicate fibers are easily damaged during ablation of hard occlusionmaterials like calcified deposits. Moreover, the light energy isattenuated over a relatively short distance as it passes through a smalloptical fiber. Thus, there is a need for new approaches to deliver lightenergy to a vascular occlusion.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention include a catheter system to ablate targetmatter within a mammalian body using light energy. The system mayinclude an open-ended catheter tip through which a liquid light guidemedium flows to the target matter, where at least a portion of theliquid light guide medium exiting the catheter tip creates a fluidoptical channel to transmit the light energy from the catheter tip tothe target matter. The system may also include a catheter lumen whosedistal end comprises the open-ended catheter tip, where the lumencontains a distal end of at least one optical fiber that transmits thelight energy to the liquid light guide medium, and where the lumen actsas a conduit for the liquid light guide medium flowing through thecatheter tip. The system may still further include a light source togenerate the light energy, where the light source is optically coupledto at least one optical fiber, and a liquid light guide medium sourcefluidly coupled to the catheter lumen, where the medium source comprisesa reservoir of the liquid light guide medium comprising a magnesiumchloride solution or a lactated Ringer's solution.

Embodiments of the invention also include a catheter system fordelivering laser light energy to target matter in a mammalian body. Thesystem may include an open-ended catheter tip through which a liquidlight guide medium flows to the target matter, where at least a portionof the liquid light guide medium exiting the catheter tip creates afluid optical channel to transmit the laser light energy from thecatheter tip to the target matter. The system may also include a lumenhaving a distal end coupled to the open-ended catheter tip, and abranched connector comprising first and second branch inlets and anoutlet coupled to a proximal end of the lumen. One or more opticalfibers may pass through the first branch of the connecter and into thelumen, where the optical fibers are optically coupled to a laser thatgenerates the laser light energy. A liquid light guide medium source maybe coupled to the second branch of the connector, where the mediumsource comprises a reservoir of the liquid light guide medium comprisinga magnesium chloride solution or a lactated Ringer's solution.

Embodiments of the invention still further include a catheter system todeliver light energy to target matter in a mammalian body. The systemmay include an open-ended catheter tip through which a liquid lightguide medium flows to the target matter, where at least a portion of theliquid light guide medium exiting the catheter tip creates a fluidoptical channel to transmit the light energy from the catheter tip tothe target matter. The system may also include a catheter lumen whosedistal end comprises the open-ended catheter tip, where the lumen actsas a conduit for the light energy transmitted though the liquid lightguide medium in the conduit. The system may further include a lightsource to generate the light energy, where the light energy istransmitted from the source to the open-ended catheter tip exclusivelythrough the liquid light guide medium in the catheter lumen, and aliquid light guide medium source fluidly coupled to the catheter lumen.

Embodiments of the invention also further include methods of deliveringlight energy to target matter in a mammalian body. The methods mayinclude the steps of positioning an open-ended catheter tip proximate tothe target matter, and flowing a liquid light guide medium comprising amagnesium chloride solution or a lactated Ringer's solution through theopen-ended catheter tip towards the target matter, where at least aportion of the liquid light guide medium exiting the catheter tipcreates a fluid optical channel to transmit the light energy from thecatheter tip to the target matter. The methods may further includeactivating a light source to generate the light energy that istransmitted through the fluid optical channel to the target matter.

Embodiments of the invention still also include a catheter system thatincludes a catheter to define a catheter lumen which acts as a conduitfor a liquid light guide medium. The catheter has an open-ended distalend through which the liquid light guide medium flows to the targetmatter. At least a portion of the liquid light guide medium exiting thecatheter tip creates a fluid optical channel to transmit the lightenergy from the catheter tip to the target matter. The system may alsoinclude an optical fiber extending into the catheter lumen and having adistal end terminating inside the catheter. The optical fiber transmitsthe light energy to the liquid light guide medium. The system mayfurther include a liquid light guide medium source fluidly coupled tothe catheter lumen. The medium source includes a reservoir of the liquidlight guide medium, which may be a magnesium chloride solution or alactated Ringer's solution.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components. In someinstances, a sublabel is associated with a reference numeral and followsa hyphen to denote one of multiple similar components. When reference ismade to a reference numeral without specification to an existingsublabel, it is intended to refer to all such multiple similarcomponents.

FIG. 1 shows an embodiment of a liquid-light guide catheter assemblyaccording to embodiments of the invention;

FIG. 2 shows a schematic of a fluid optical channel formed between anopen-ended catheter tip and a vascular occlusion according toembodiments of the invention;

FIG. 3 shows a schematic of a catheter system with a segmented distalportion according to embodiments of the invention;

FIG. 4 shows a schematic of a catheter system that uses a liquid lightguide medium to transmit light energy through the catheter lumenaccording to embodiments of the invention;

FIG. 5 shows a branched connector for a catheter system that contains anoptical fiber according to embodiments of the invention;

FIG. 6 is a flowchart illustrating selected steps in methods ofdelivering light energy to target matter according to embodiments of theinvention;

FIGS. 7A-C are plots of the refractive index versus concentration forsolutions of magnesium chloride, calcium chloride, and sodium chloride.

DETAILED DESCRIPTION OF THE INVENTION

Catheter systems are described that use a liquid-phase light guide totransmit light energy to target matter (e.g., an occlusion) inside amammalian body (e.g., an occlusion site inside the vasculature of ahuman patient). The catheter systems have an open-ended catheter tipthat directs a liquid light guide medium from the end of the catheter tothe target matter. The flow of light guide medium out of the cathetertip creates an optical fluid channel between the medium and thesurrounding blood. The difference in the indices' of refraction betweenthe medium and the blood are large enough to facilitate total internalreflection of the light energy transmitted from the catheter tip to thetarget medium.

The liquid light guide medium is a biocompatible fluid that hasexcellent light energy transmission characteristics at the lightwavelengths used. For example, a light source that is particularlycapable of ablating calcified, fibrotic occlusions is the XeCl Excimerlaser, which transmits laser light energy around the 308 nm wavelength.It has been discovered that solutions of magnesium chloride and lactatedRinger's solution are very effective for liquid light transmission atthis wavelength. Moreover, these solutions have excellentbiocompatibility when they are introduced into a patient. For example,the ion concentrations of these solutions may be set to achieve anisotonic state with blood and tissue. This helps avoid hemolysis, whichcan be caused when hypotonic pure water substitutes for the isotonicsolutions.

Magnesium chloride and lactated Ringer's solutions are also less toxicthan other salts that may be used as liquid light guide mediums. Forexample, solutions of calcium chloride (CaCl₂) are normally moreconcentrated than a comparable magnesium chloride solution with an indexof refraction between about 1.37 and 1.42. Calcium chloride solutions atthese concentrations are less biocompatible, and may cause necrosis ifintroduced to a patient's muscle tissue. However, magnesium chloridesolutions are biocompatible at the concentration needed to achieve asimilar index of refraction.

Exemplary Catheter Systems

FIG. 1 shows an embodiment of a liquid-light guide catheter assembly 100according to embodiments of the invention. The catheter assembly 100includes a Y-connector 102 having branched proximal ends 104 and 106that merge into a single distal end 108. One proximal end is coupled toa light source (not shown) which generates light energy that istransmitted through the catheter assembly to the target matter. Theother proximal end is fluidly coupled to a source 110 for the liquidlight guide medium that transmits the light energy and forms a fluidoptical channel for transmitting the light energy from the end of theassembly 100 to the target matter.

The distal end 108 of the Y-connector 102 is coupled to a proximal endof a catheter lumen 112. The distal end of the lumen 112 is open endedso the liquid light guide medium can exit the catheter assembly 100 andform the fluid optical channel between the assembly and target matter.The lumen 112 may also provide a path for an guidewire (not shown) todirect the distal end of the lumen to a position proximate to the targetmatter. The lumen interior may also accommodate an optical fiber 114that transmits light energy from the light source to a distal end of thefiber. The fiber's distal end may terminate inside the lumen 112 wherelight energy exits the fiber 114 and is transmitted through the liquidlight guide medium to the distal end of the lumen and then through thefluid optical channel to the target matter.

The catheter tubing may be made from flexible, biocompatible materialswith refractive indices that facilitate total internal reflection at thewavelengths of light energy used. For example, the tubing may be madefrom a material with an index of refraction that is lower than theliquid light guide medium flowing through the lumen. Examples ofmaterials that fulfill these criteria at the 308 nm wavelength includefluoropolymers (e.g., fluorinated ethylene propylene (FEP) orpolytetrafluoroethylene (PTFE) material) with refractive indices belowthat of water, such as Teflon® AF2400™ and Teflon® FEP from DuPont.

The liquid light guide medium may be selected for its efficienttransmission of the light energy at the wavelengths generated by thelight source. For example, embodiments of the present invention includean Excimer laser using a xenon chloride (XeCl) lasing medium as thelight source. A XeCl Excimer laser generates laser light energy with awavelength of about 308 nm, so a liquid light guide medium is selectedfor efficient transmission around this wavelength. Liquid mediums withexcellent transmittance at this wavelength include aqueous magnesiumchloride solutions, such as solutions of pure magnesium chloride,solutions of anhydrous magnesium chloride, and solutions of hydratedmagnesium chloride (e.g., magnesium chloride hexahydrate). They alsoinclude Lactated Ringer's solution, which may include aqueous ions ofsodium, chloride, potassium, calcium and lactate. The sources of theseions in a lactated Ringer's solution may come from sodium chloride(NaCl), sodium lactate (NaC₃H₅O₃), calcium chloride (CaCl₂), andpotassium chloride (KCl), though as will be appreciated by one of skillin the art, other combinations of salts may be used. As noted above,both magnesium chloride and lactated Ringer's solution have excellentbiocompatibility (e.g., low toxicity) as well as excellent lighttransmission characteristics at the 308 nm wavelength.

FIG. 2 shows how the liquid light guide medium flowing from the distalend of catheter lumen forms a temporary fluid optical channel 202between the catheter tip 204 and a vascular occlusion 206. In thisillustration, the tip of the catheter lumen 204 is positioned adjacentto the vascular occlusion 206 that represents the target matter. Theliquid light guide medium is then pumped out the distal catheter tip 204to establish the fluid optical channel 202. The liquid light guidemedium may be supplied from a source (not shown) that is fluidlyconnected to a proximal end of the catheter lumen and pumped through thelength of the lumen.

When the fluid flow reaches the vascular occlusion 206 and establishesthe fluid optical channel 202, a light source (not shown) may beactivated to transmit light energy through the medium in the catheterand the channel 202 into the occlusion 206. When the light source is aXeCl Excimer laser, the light energy may be a high energy pulse of 308nm laser light that can ablate material from the occlusion 206.

The liquid light guide medium is selected to create total internalreflection of the light energy transmitted through the fluid opticalchannel 202. Total internal reflection may be established when the angleof incidence of the light transmitted through the lumen of the tubinghas an angle with the normal surface of the tubing (or blood surroundingthe fluid optical channel) satisfies the condition for total internalreflection defined by the fact that the angle of incidence is greaterthan a critical angle d established by the ratio of the index ofrefraction of the medium (n₁) and the surrounding blood (n₂) as follows:

${\sin\; d} = \frac{n_{2}}{n_{1}}$Thus, increasing the difference in the index of refraction between thecore and surrounding blood increases the angle at which off-axis rayscan be conducted in the core and minimizes losses arising from bends intortuous arteries. In addition, the medium should not have significantoptical absorption or scattering at the wavelength of the light energy.

Biocompatible concentrations of magnesium chloride and lactated Ringer'ssolutions have indices of refraction (n) in the range of about 1.33 toabout 1.42 for 308 nm light energy. These refractive indices can be madedifferent enough from the refractive index of blood (where n istypically about 1.34-1.36) to establish a high level of internalreflection for the 308 nm light energy transmitted through the fluidoptical channel. In effect, the blood will act as the cladding materialfor the fluid optical channel established by the flowing optical lightguide medium.

When the light ablation forms an indentation or cavity in the targetmatter, the remaining matter (i.e., tissue) can form a cladding surfacefor the fluid optical channel. Like blood, bodily tissue normally has alower index of refraction than the liquid light guide medium and mayfacilitate total internal reflection of the light energy traveling inthe fluid optical channel. Thus, ablating the target material mayprogress from a fluid optical channel formed from a liquid light guidemedium core surrounded by blood, to a channel formed by the liquid lightguide medium flowing into an opening or cavity formed in the ablatedtarget material. This may allow the efficient transmission of the lightenergy deep into a vascular occlusion.

Referring now to FIG. 3, a schematic of another catheter system 300 witha segmented distal portion according to embodiments of the invention isshown. The distal part of this system includes an open-ended distal tip302 made from a tubing segment 304 that is coupled at its proximal endto a piece of shrink tubing 306 that connects the tubing segment 304 toa second piece of shrink tubing 308, which in turn is coupled at theopposite end to the distal end of catheter lumen 312. Tubing segment 304may have an outer diameter that is smaller than the inner diameter ofshrink tubing 306, so it can be inserted into the shrink tubing. Forexample, the first segment may be about 1 cm long piece of tubing withan inner diameter greater than about 0.7 mm. Tubing segment 304 andshrink tubing pieces 306, 308 together form a conduit for a liquid lightguide medium and optical fiber 309.

The catheter lumen 312 provides a fluid conduit for a liquid light guidemedium that may be pumped through the lumen from a fluid source 314coupled to the Y-connector 316 of the system 300. As the medium exitsthe distal end of the lumen 312 it travels through the pieces of shrinktubing and tubing segment 304, respectively, and out the distal tip 302.

A tail tube 318 may also be coupled to the Y-connector 316 to provide aconduit for liquid light guide medium and/or optical fiber between asource (not shown) and the Y-connector. When an optical fiber isprovided, light energy from the light source travels through the fiberinside the tail tube 318 and Y-connector 316 to the open-ended catheterlumen 312. Alternatively, the tail tube 318 may transmit light energyusing a liquid light guide medium in lieu of (or in addition to) anoptical fiber. The distal end optical fiber may terminate beforereaching the lumen 312, or inside the lumen 312. In both instances, thelight energy originally traveling thought the fiber may continue throughthe liquid light guide medium in the lumen.

The optical fiber 309 may extend completely through the lumen 312 andsecond piece of shrink tubing 308, as shown. In this embodiment, thedistal end of the optical fiber terminates inside the tubing segment304, where the liquid light guide medium allows the light energy totravel to the distal end 302 before continuing through a fluid opticalchannel to the target matter. Additional embodiments may include havingthe optical fiber extend to the distal tip 302 or beyond the distal tip.The optical fiber may be made from and coated with a cladding materialappropriate to transmit light at the wavelength of the light energy(e.g., about 308 nm) and may have a size about 300 μm to about 600 μm indiameter (e.g., 600 μm in diameter), or a bundle of fibers ranging from50 μm to 130 μm core diameter in a quantity that fits within the lumenof the tubing. The bundle of small core-sized optical fibers can provideadditional flexibility and tortuosity to maneuver around tight curves ina patient's vasculature.

The tubing segment 304 may be made from flexible, biocompatiblematerials with refractive indices that facilitate total internalreflection at the wavelengths of light energy used. As noted above,examples of materials that fulfill these criteria at the 308 nmwavelength include fluoropolymers (e.g., fluorinated ethylene propylene(FEP) or polytetrafluoroethylene (PTFE) material) with refractiveindices below that of water, such as Teflon® AF2400™ and Teflon® FEPfrom DuPont. The pieces of shrink tubing 306, 308 may be made from, forexample, polyamide polymers. In addition, the catheter lumen 312 may bemade from a fluoropolymer, or some other material with the appropriateflexibility, biocompatibility and refractive index facilitating wallreflection to enable the transmission of the light energy through theliquid light guide medium.

FIG. 4 shows an embodiment of a catheter lumen 402 that relies on aliquid light guide medium to transmit light energy. The catheter lumen402 has a wall 404 that encloses the lumen 406. The lumen functions as aflow channel for liquid light guide medium 408 traveling from theproximal end 410 to distal end 412. Light energy travels through themedium by reflecting off the inner lumenal surface 414 at an angleconducive to total internal reflection. Still, some of the light energyis attenuated as it moves from the proximal end 410 (indicated by arrow“I”) of the catheter lumen 402 out the distal end 412 (indicated byarrow “O”). The magnitude of the attenuation depends on thecharacteristics of the liquid light guide medium as well as thecharacteristics of the tube wall and the number of the curves in thepath of the lumen. The illustrated embodiment shows catheter lumen 402having a circular cross-section, and may have transverse dimensionsbetween about 0.5 mm to about 3 mm (e.g., about 0.7 mm to about 0.9 mm).

The materials used for wall 404 are selected in part based on therefractive index (n_(w)) of the wall of the inner lumenal surface 414.The refractive index n_(w) should be less than the refractive indexn_(f) of the liquid light guide medium traveling through the lumencatheter 402. In other words, the ratio of the fluid refractive index(n_(f)) to the lumen wall refractive index (n_(w)) (i.e., n_(f)/n_(w))is greater than 1.0. For example, the value of n_(f)/n_(w) may be about1.05 or more, about 1.1 or more, about 1.15 or more, etc.

The materials used for wall 404 are also selected in part to providestructural strength as well as flexibility so that the liquid-filledlight guide may be bent through sharp curves without kinking orsubstantially distorting the cross-sectional geometry of the catheterlumen 402. These materials may include commercially availablefluorinated ethylenepropylenes such as Teflon® FEP from DuPont, whichhas a relatively low refractive index of about 1.33, or Teflon-AF2400,which has an index of refraction of about 1.30.

FIG. 5 shows additional details of a branched Y-connector 500 for acatheter system according to embodiments of the invention. TheY-connector 500 includes a main barrel 502 whose distal end 504 iscoupled to a catheter lumen 506. There is also a second branch 508extending from the barrel 502 that establishes as fluid conduit betweena liquid light guide medium source 504 and the Y-connector 500. Thesecond branch 508 terminates at an inlet for liquid light guide mediumto enter the Y-connector 500. The second branch may also include abubble filter 511 between the source 504 and main barrel 502 thatprevents bubbles in the medium from flowing into the barrel 502.

The proximal end 512 of the main barrel 502 has an inlet 514 for anoptical fiber 516. The optical fiber 516 is used to transmit lightenergy into the catheter lumen 506 from a light source (not shown)optically coupled to the proximal end of the optical fiber 516. Theinlet 514 may include an o-ring 515 that forms a fluid tight sealbetween the optical fiber 516 and barrel 502 to prevent liquid lightguide medium from leaking out the proximal end 512, even when theoptical fiber is being advanced or retracted in the Y-connector 500.

The distal end 518 of the optical fiber 516 is inserted through theproximal end 512 of the barrel to the catheter lumen 506. The fiber 516may be advanced all the way to (or even through) the distal end of thelumen 506 (not shown), or may be advanced to a point behind the distalend of the lumen. When the optical fiber 516 is positioned proximal tothe distal end of the lumen 506, light energy emitted from the tip ofthe fiber will travel through liquid light guide medium in the lumen 506before exiting the catheter.

Exemplary Methods of Delivering Light Energy

FIG. 6 shows a flowchart illustrating selected steps in methods ofdelivering light energy to target matter according to embodiments of theinvention. These steps may include providing a catheter lumen with anopen-ended distal tip 602. The open-ended tip permits a liquid lightguide medium to flow out of the catheter. At least a portion of thelumen, including the distal tip, is inserted into a patient'svasculature 604. The lumen may then traverse the vasculature until thedistal tip is positioned proximate to target matter 606, such as avascular occlusion. Embodiments include using a guidewire to help guidethe lumen tip through the vasculature to the site of the target matter.

When the distal tip of the lumen is in position, a liquid light guidemedium may flow through the catheter and tip 608. As the medium flowsout of the catheter tip towards the target matter, it forms a fluidoptical channel between the catheter and target 610. The core of thisoptical channel is the liquid light guide medium with its index ofrefraction. The patient's blood that surrounds the medium establishes afluid optical cladding with a second index of refraction. A liquid lightguide medium is selected so that the ratio of the index of refractionfor the medium to the index of refraction for the surrounding blood isat least about 1.0, (e.g., least about 1.05, at least about 1.10, etc.).

The fluid optical channel provides a temporary optical path for lightleaving the catheter to reach the target matter. Thus, the formation ofthe fluid optical channel is coordinated with activating a light source612 that generates light energy for transmission through the catheterand fluid optical path to the target matter. As noted above, the lightsource may be a XeCl Excimer laser that generates a pulse of laser lightat about 308 nm. The duration of the pulse may be shorter than theeffective lifetime of the fluid optical channel.

When the light energy reaches the target material, it causes theablation of the target material 614. In some embodiments, a single pulseof laser light energy may be sufficient to ablate the occlusion andreopen (or further open) a blood vessel. Alternatively, multiple cyclesof fluid optical channel formation and light pulses may be performed tofully treat the target matter (e.g., fully open a blocked blood vessel).

EXPERIMENTAL

Indices of refraction for three aqueous salt solutions were measured asa function of the salt concentration in solution. The three salts weremagnesium chloride hexahydrate (MgCl₂·6H₂O), calcium chloride (CaCl₂),and sodium chloride (NaCl). FIGS. 7A-C are plots of the refractive indexversus salt concentration for the three solutions. FIG. 7A shows thatincreasing the concentration of a magnesium chloride hexahydratesolution from near 0% weight of the solution to 30% weight increases itsindex of refraction from about 1.335 to about 1.415. FIG. 7B shows thatincreasing the concentration of a calcium chloride solution from near 0%wt. to 15% wt. increases its index of refraction from about 1.335 toabout 1.370. Finally, FIG. 7C shows that increasing the concentration ofa sodium chloride solution from near 0% wt. to about 3% wt. increasesits index of refraction from about 1.3332 to about 1.3385.

First derivates of the three lines plotted for FIGS. 7A-C indicate thatthe largest increase in the index of refraction per unit percentageincrease in concentration occurred with the magnesium chloridehexahydrate solution (First Derivative=0.0027) compared with the calciumchloride solution (First Derivative=0.0025) and sodium chloride solution(First Derivative=0.0018). Because the refractive index of the magnesiumchloride solution is more sensitive to changes in salt concentration,less concentrated solutions may be used to produce a high enoughrefractive index to cause total internal reflection between the liquidand the surrounding catheter lumen material or blood (i.e., thesurrounding optical cladding material).

Additional experiments were run to record the absorption spectra of thethree salt solutions at and around the wavelengths of light generated bya XeCl Excimer laser (i.e., around 308 nm). The absorption spectra wererecorded for a wavelength range from 305 nm to 310 nm the absorptionpeaks for each of the aqueous ions (i.e., Mg²⁺, Na⁺, Ca²⁺, Cl⁻) arelisted in Table 1 below:

TABLE 1 Measured Absorption Peaks for Selected Aqueous Salt Ions from305-310 nm Measured Absorption Peaks Number of Absorption Aqueous Ion(305-310 nm) Peaks Mg²⁺ 307.423, 308.0208, 309.1065, 5 309.2984,309.6890 Na⁺ 305.3665, 305.5354, 305.6160, 16 305.7375, 305.8715,306.4374, 306.6534, 307.0566, 307.0823, 307.832, 307.8747, 308.0251,308.7057, 309.2731, 309.4449, 309.5546 Ca²⁺ 307.157, 307.695, 308.079, 4309.930 Cl⁻ 306.313, 307.136, 307.688 3

Table 1 indicates that sodium ions (Na⁺) have about 3 to 5 times thenumber of absorption peaks in the 305-310 nm wavelength range thanmagnesium, calcium or chloride ions. This correlates with the measurablyhigher absorbance rates for XeCl Excimer laser light that use a sodiumchloride solution (an ingredient in standard buffered Saline solution)for a liquid light guide medium. The higher absorbance results in lessof the light energy reaching the target matter (i.e., higher lightattenuation).

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a method” includes aplurality of such methods and reference to “the lumen” includesreference to one or more lumens and equivalents thereof known to thoseskilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A method of delivering light energy to targetmatter in a mammalian body, the method comprising: positioning anopen-ended catheter to face the target matter inside the mammalian body;pumping a liquid having an ion concentration that is isotonic withmammalian blood from a reservoir and through the open-ended catheter tothe target matter, and creating a liquid optical channel between thecatheter and the target matter with the liquid, the liquid opticalchannel surrounded by blood in the body to transmit the light energyfrom the catheter to the target matter through the liquid opticalchannel; activating a light source to generate the light energy; andtransmitting the light energy through the liquid optical channel to thetarget matter by total internal reflection and ablating the targetmatter with the light energy, wherein the light energy has a wavelengthin a range of 305-310 nm, the liquid includes magnesium and chlorideions and has an index of refraction in a range of 1.33-1.42 for thewavelength, and the index of refraction of the liquid is at least 5%higher than an index of refraction of the catheter and is higher than anindex of refraction of the blood in the body.
 2. The method of claim 1,wherein the liquid comprises a magnesium chloride solution and has anindex of refraction between 1.33 and 1.42 for 308 nm light energy. 3.The method of claim 2, wherein the magnesium chloride solution comprisesmagnesium chloride hexahydrate and has an index of refraction between1.33 and 1.42 for 308 nm light energy.
 4. The method of claim 1, whereinthe liquid medium comprises one of aqueous magnesium chloride solutions,pure magnesium chloride solutions, solutions of anhydrous magnesiumchloride, and solutions of hydrated magnesium chloride.
 5. The method ofclaim 4, wherein the method further comprises forming a cavity inremaining target matter after the ablation, where the cavity provides acladding surface to extend the liquid optical channel into the remainingtarget matter and wherein the light.
 6. The method of claim 1, whereinthe light source is a XeCl Excimer laser and the light energy has awavelength of 308 nm.
 7. The method of claim 1, wherein the methodfurther comprises exclusively transmitting the light energy through theliquid from the light source to the open-ended catheter.